The majority of food banks get discounted supplies. They seldom pay full retail price. In some cases I know about, distributors and retailers will sell older perishable stock to food banks when they don't think they can move it quickly enough.

The trouble with food vouchers is that junkies trade them for drugs. Vouchers are more "liquid" than physical food.

No. They were paying full price, I specifically checked.

I mean the junkies could just use the money they didn't spend buying food to buy drugs. I'm not entirely sure this isn't just an extension of people feeling like they're doing a good thing rather than actually doing a good thing. And that's assuming a meaningful proportion of food bank users are actually junkies.